This invention relates in general to new and useful improvements in jigs, and more particularly to an improved jig for forming assemblies such as roof trusses which may vary greatly in configuration.
Wooden trusses such as roof trusses are commonly assembled on large horizontal tables supported by any suitable means at working height above a shop floor. Heretofore, stops have been laid out and affixed to the table surface using tape measures and chalk lines to provide a jig setup defining the truss to be assembled. In the case of wooden table surfaces, the stops comprise wood blocks nailed in place. The less-common steel surfaces are perforated to provide bolt holes spaced at six-inch intervals. Stop fixtures are bolted in place using these holes, the fixtures being adjustable to locate stops carried thereby more precisely.
These systems, though inefficient, have been acceptable because until recently the same jig setup was used to assemble 35 to 40 or more identical trusses in succession. Now, however, architects and builders tend to design and construct unique or "custom" residences and commercial buildings with little regard for standardized roof dimensions and configurations, and it is therefore not unusual for a truss manufacturer to receive orders for as few as four or five trusses in a given pattern. In the face of such small numbers, the foregoing conventional methods of laying out jig setups become extremely expensive procedures. Further, when a builder requires additional trusses in a given pattern after the jig setup has been removed or altered, in order to be certain that the pattern and dimensions are precisely duplicated, it has been necessary to return one of the previously made trusses to be used as a template for reproducing the jig setup.
An expedient intended to reduce the time required for setting up truss jigs has recently been developed in which recessed channels are spaced at equal intervals in parallel across the jig table surface, each channel supporting a stop at surface level, the stop being movable along the length of the channel by means of a worm drive which includes a threaded shaft extending longitudinally within the channel. Each channel originates at an edge of the table, extending inwardly therefrom to terminate short of the opposing edge. Alternate channels originate at opposite edges. The threaded shafts are rotated by means of an air wrench to position the stops. For a given truss configuration, the location of each stop along the length of the respective channel is indicated by a computer readout in terms of the equivalent number of revolutions of the corresponding threaded shaft. A meter or counter is provided at the edge end of the shaft so that the operator may rotate the shafts until the counter readings are matched with the respective numbers provided by the computer readout. Such an installation is not only extremely expensive, but is necessarily limited to only a single stop per channel.
U. S. Pat. No. 4,943,038, issued July 24, 1990 in the name of C. W. Harnden and assigned to Alpine Engineered Products, Inc., is directed to apparatus of the foregoing description.